Tell how to undo each operation and explain why it works. adding 28. dividing by 17

Addition: Use subtraction, because the inverse of adding is subtracting. Same goes for subtracting. Add.

Multiplying: Opposite to divideing

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since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.